2D-IR experiments are proposed to study the equilibrium structure and dynamics of the transmembrane protein Glycophorin A (GpA) in several lipid bilayer environments. Glycophorin A dimerizes through weak van der Waals forces and CaH...O hydrogen bonds. It is expected that these weak associations are easily disrupted as the environment is changed. Thus, 2D-IR studies examining the interactions between the residues on opposite strands will reveal information about how the structure of GpA changes as the environment changes. Several lipid bilayers will be studied, both a dimyristoylphosphatidylcholine (DMPC) membrane vesicle and a DMPC/cholesterol vesicle, to probe how lipid composition influences the structure, and thus function, of transmembrane protein. This work will test hypotheses about the role of lipid microdomains or "rafts" on protein structure. Single and Dual Frequency 2D-IR photon echo experiments will be performed on isotopically labeled GpA in different lipid phases to determine which interactions are most sensitive to environment. Transmembrane proteins are not easily probed by conventional techniques, and the influence of membrane composition on transmembrane structure and function is not well understood. Since many transmembrane proteins critical to cell function, understanding the interplay between membrane environment and protein structure is vitallv important.